CA2689878C - Use of a tio2 composition for the recovery of halogenated compounds contained in a gas mixture - Google Patents

Abstract

The invention concerns the use of a compound upstream from a Fischer-Tropsch synthesis unit, and jointly as a capture system to eliminate halogenated impurities contained in a gaseous mixture and as a catalyst allowing the hydrolysis of COS and/or HCN to be carried out, the said compound including between 30% and 99% weight of TiO2 and between 1% and 30% weight of at least one sulfate of an alkaline earth metal selected among calcium, barium, strontium and magnesium.

Description

OF HALOGEN COMPOUNDS CONTAINED IN A GASEOUS MIXTURE
The present invention relates to the field of gaseous mixture purification such as example, the synthesis gas used in cogeneration units, processes of Fischer-Tropsch synthesis, chemical synthesis processes, or even batteries fuels. It concerns more particularly the use of a composition based on TiO2 as a capture mass to eliminate halogenated impurities such as by example HF, HCI, HBr, and / or HI.
Prior art Synthetic gas can conventionally be obtained by transformation of the gas natural, from coal, heavy oil residues or biomass by processes such as that the steam reforming, autothermal reforming, or partial oxidation, or by decomposition of methanol.
This is usually a mixture of carbon monoxide, hydrogen, from water vapor and carbon dioxide, in varying proportions depending on the process of synthesis gas production used. Depending on the type of charge from of which he is obtained, the synthesis gas additionally contains impurities, such as by example of sulfur compounds, nitrogen compounds, halogenated compounds, and / or metals.
In particular, there are significant contents of halogenated compounds, such as by example HF, HCI, HBr and / or HI, in the synthesis gas from the gasification of the biomass, coal, petroleum residues, alone or as a mixture ("co-processing "according to the Anglo-Saxon terminology).

the The contents of halogenated compounds initially present in the feedstock gasify can reach 1000 ppm weight in the case of coal or even 10000 ppm weight in the case of biomass according to its nature and geographical origin. These compounds present in the charge are found in the gas after conversion.
The halogenated compounds present in the unpurified synthesis gases can lead to accelerated corrosion of the installations in which they are used, such as by example gas turbines in cogeneration units (IGCC or "Integrated Gasification

2 Combined Cycle "in English terminology.) Cogeneration allows the production of electricity and useful thermal energy in the form of steam water or gas combustion from a fuel, such as, for example, natural gas, biomass, the coal. The gases resulting from a cogeneration installation must meet specification particular, related to downstream process requirements. The halogens are thus constituents often encountered that it is necessary to eliminate effectively.
Halogenated impurities are also likely to poison catalysts set in Fischer-Tropsch synthesis processes or in synthesis chemical processes such as methanol synthesis processes, or to mitigate the performance of materials used in fuel cells.
As such, the requirements in terms of purity of the gases are very severe. he is therefore to eliminate these halogenated impurities, besides the other types of impurities that are suitable also to eliminate, so that the gas contains only contents these contents residuals being generally less than 10 ppb each component.
The purification can be carried out by means of processes implementing the use of solvents or capture masses.
The solvent washing technique generally requires the use of a basic solvent in order to remove the halogenated acidic compounds from the gas to be treated. For this reason, several types of solvent can be used. Solvents containing amines such as monoethanolamine (MEA), diethanolamine (DEA) or methyldiethanolamine (MDEA), classically used for the removal of acid gases such as for example H 2 S or CO2, can also be used for the removal of halogenated compounds. In this case, the compounds to be removed react chemically with the solvent. In the case of the use of DEA, it is also possible to eliminate COS, at 50% for elimination thrust stage of hydrolysis of COS in H2S being necessary upstream of the column absorption. HCN
is also eliminated, at the expense of irreversible degradation solvent. The water

3 possibly in the presence of sodium hydroxide may also be used to the elimination of halogenated impurities.
The RectisolTM process can also be used for the removal of gases acids. The purification is carried out by carrying out an extraction with methanol Has very low temperatures (-40 to -60 C). This process also allows the elimination of others impurities such as sulfur compounds, as well as nitrogen compounds (NH3, HCN), and heavy metals such as arsenic and mercury.
It can also be used processes using solvents physical that solvents based on polyethylene glycol dialkyl ether mixtures, or those using mixed physical and chemical solvents such as amine mixtures and sulfolane.
These washing processes generally operate at temperatures between -80 C and 250 C, depending on the type of solvent used.
Processes using capture masses are more suitable for purification of hot gases. In this case, the gas treatment does not necessarily require lowering of the temperature of it and is therefore energetically more economical.
classically, capture masses such as dolomite-based solids, zeolites, aluminas alkaline metals, or even oxides of zinc, can be used.
The use of treated aluminas is the most common way of purifying gases high temperature.
For example, US Pat. No. 6,200,544 describes an adsorbent to eliminate HC1 in gases, the adsorbent comprising an activated alumina impregnated with an oxide alkaline and doped with phosphates and / or organic amines.
WO 1999/40999 discloses a process using an adsorbent for the elimination of halogenated compounds, such as hydrogen chloride (HC1), present in loads gaseous or liquid, the adsorbent being obtained by depositing on an alumina of minus one selected from alkalis, or from alkaline earths and earths rare. The

4 preparation of the adsorbent is completed by calcination at a temperature of less equal to 500 C or 600 C depending on the nature of the dopant.
EP 0 948 995 relates to a process for the elimination of halogenated present in gaseous or liquid phase operated using an adsorbent constituted of an alumina and at least one element selected from Group VIII, IB and IIB metals of the classification periodical, with a metal element content of not more than 45%
by weight relative to the total weight of the composition.
The disadvantages related to the use of basic or treated aluminas metals alkalis generally relate to either their chlorine capture capacity insufficient (the most often of the order of 8% weight), or at their temperature of use very often limited to 150 C, which implies a cooling of the gas before treatment.
The Applicant has discovered that by using a mass of capture particular, based on TiO2 and comprising at least 1% by weight of at least one sulphate of a metal alkaline earth chosen from calcium, barium and magnesium, it is possible to eliminate the impurities halogenated such as for example HF, HC1, HBr, and / or HI with a very good effectiveness of capture. It has been found that by using the composition according to the invention, a mixture gas initially containing these impurities at levels generally of 0.1 at 1000 ppm weight, preferably between 10 and 10,000 ppm by weight, can be purified so as to no longer contain than halogenated impurity contents of less than 10 ppb, or even less than 5 ppb weight.
The use of the particular composition as described in present invention can advantageously be carried out at temperatures up to 350 C and this made, requires little or no lowering of the gas temperature from a unit of production of synthesis gas before purification.
In addition, another advantage lies in the catalytic properties of the mass of capture implementation, in particular with respect to the hydrolysis properties of COS and HCN described in the patent FR 2 830 466 of the applicant. The capture of compounds halogenated =
does not result in deactivation of the mass and it presents a good stability opposite hydrolysis reactions of COS and HCN in the presence of these compounds.
Another advantage relates to the implementation of the invention for the purification of gases from

5 synthesis used in Fischer-Tropsch units since the conditions implementation of these units and the method or the use according to the invention are very Similar.
This solid can also be used in the purification of synthesis gas usable in cogeneration plants, chemical synthesis processes such as processes of synthesis of methanol, or fuel cells.
Summary of the invention The invention relates to the use of a composition based on Tia) for the capture of halogenated compounds contained in a gaseous mixture, said composition including between 10% by weight and 100% by weight of TiO2 and between 1% by weight and 30% by weight of at least one sulfate of a alkaline earth metal selected from calcium, barium, strontium and magnesium.
The invention therefore relates to a process for purifying a gaseous mixture implementing said composition and for removing said halogenated impurities. In in addition, said method simultaneously hydrolyzes COS and HCN
More particularly, the invention relates to the use of a composition upstream of a Fischer-Tropsch synthesis unit, and jointly as a capture mass to eliminate the halogenated impurities contained in a gaseous mixture and as a catalyst allowing to perform the hydrolysis of COS and / or HCN, said composition comprising between 30% weight and 99% by weight of TiO2 and between 1% by weight and 30% by weight of at least one sulfate of metal alkaline earth selected from calcium, barium, strontium and magnesium.

5a detailed description The subject of the invention is the use of a composition (also called mass of capture) based on TiO2 to eliminate (capture) the halogenated impurities such as by example HF, HC1, HBr and / or HI contained in a gaseous mixture such as preferably a synthesis gas, or any other gas capable of contain halogens, such as hydrogen used in refineries, or gases natural synthetic.
The invention therefore relates to a process for purifying a gaseous mixture implementing said composition and for removing said halogenated impurities.

6 When the gas mixture is a synthesis gas, it may advantageously be obtained through the transformation of biomass alone or with added coal, gas natural or oil residues by processes such as partial oxidation or steam reforming, or from any other method known to those skilled in the art. It includes at least of hydrogen and carbon monoxide.
When the gaseous mixture is a synthesis gas used in the synthesis Fischer-Tropsch it most often has a molar ratio H2 / CO between 0.5 and 5.0, preferred way between 1.2 and 3.1 and even more preferably between 1.5 and 2.6. The gas of synthesis usually includes in addition a small proportion of carbon (CO2), preferably less than 15% by volume, or even less than 10% by volume, and that eventually water vapor ..
When the gaseous mixture is a cogeneration gas, it presents the most often volume concentrations of between 10 and 40% by volume for hydrogen, between 15 and 70% by volume for carbon monoxide (CO), between 200 ppm and 5% by volume for the hydrogen sulphide (H2S), between 0.5 and 25% by volume for H20, and possibly carbon dioxide.
In general, syngas also includes many impurities such as sulfur compounds (H2S, COS, CS2), nitrogenous (NH3, HCN), halogenated (HF, HC1, HBr, HI), and also metals, such as for example mercury, selenium and metals carbonyls.
Levels of impurities present in the gas after the gasification are according to the nature of the load used. More particularly, the contents of compounds halogenated be between 10 and 1500 ppm by weight or between 50 and 1000 ppm weight. the contents of sulfur compounds may be of the order of 20 to 15000 ppm by weight, see from 100 to 10000 ppm weight.

7 The raw synthesis gas, directly from gasification and having possibly been subjected to a step of converting carbon monoxide to water vapor (water gas shift according to English terminology) in order to adjust the H2 / CO ratio, is usually sent to one or more purification steps dedicated to the elimination of metals present as well most of the compounds are sulfur, nitrogen and halogenated. There where said steps are generally performed by washing with a solvent.
Solvent washing is generally carried out using a solvent containing at least an amine such as for example monoethanolamine (MEA), diethanolamine (DEA) or methyldiethanolamine (MDEA), or a solvent containing at least one alcohol such that the methanol. Solvents based on polyethylene dialkyl ether blends glycol (PEG) such PEG diethyl ether or dibutyl ether may also be employed, or mixed physical and chemical solvents such as those obtained, for example, from from mixtures of an amine, such as MDEA or diisopropanolamine (DIPA), with of sulfolane and water.
Following this treatment, the levels of impurities contained in the gas of synthesis reach generally from 0.1 to 50 ppm by weight for halogenated compounds, 0.1 to 50 ppm weight for PH2S, 0.1 to 50 ppm weight for COS, 0.1 to 50 ppm weight for the nitrogen compounds.
The elimination of halogenated compounds present in the synthesis gas may to be operated in upstream or downstream of the previous purification step, or any other purification step possibly implemented.
According to the invention, the elimination of the halogenated compounds is carried out in using a ' composition based on TiO2 as a compound uptake mass halogenated, said composition comprising between 10% by weight and 100% by weight of TiO2 and between 1% by weight and 30 % by weight of at least one sulphate of an alkaline earth metal selected from calcium, barium, strontium and magnesium. Said sulphate is preferably sulphate of calcium.

8 According to a preferred embodiment, the composition comprises between % weight and 99 % by weight of TiO 2, more preferably between 45% by weight and 98% by weight, very preferably between 60% by weight and 95% by weight, or even between 70% by weight and 90%
%weight.
Preferably, said composition comprises between 3% by weight and 25% by weight and way more between 5% by weight and 15% by weight of at least one sulphate of an alkali metal earthy chosen among calcium, barium, strontium and magnesium. Said sulphate is preferentially calcium sulphate.
Preferably, the composition also comprises at least one selected compound from clays, silicates, aluminas, titanium sulphate, fibers ceramics, preferably clays or silicates, possibly aluminas, in a very favorite clays, at a total content of between 0.1% by weight and 30% by weight, preferably between 0.5 % by weight and 25% by weight, more preferably between 1% by weight and 20% by weight.
% weight, and very preferably between 5% weight and 15% weight.
Preferably, the composition further comprises 0.1 to 20% by weight of preference between 0.5% by weight and 15% by weight and more preferably between 1% by weight and 10%
% weight, of a doping compound or a combination of doping compounds selected from composed of iron, vanadium, cobalt, nickel, copper, molybdenum and tungsten. The Doping compounds are preferably in the form of oxides or sulfides.
Preferably said doping compound is iron, vanadium, nickel or molybdenum, very way preferred iron or vanadium.
In a particularly advantageous variant of implementation, the composition includes:
between 60% by weight and 95% by weight, or even between 70% by weight and 90% by weight, of oxide of titanium, between 3% by weight and 25% by weight, or between 5% by weight and 15% by weight sulfate of a alkaline earth metal selected from calcium, barium, strontium and magnesium, between 0.1% by weight and 20% by weight, or even between 1 and 10% by weight of doping compound or a combination of doping compounds selected from iron compounds,

9 vanadium, cobalt, nickel, copper, molybdenum and tungsten, by example in the form of oxide or sulfide.
The composition according to the invention may be prepared by any known method man's job. The contribution of dopant (s) may for example be made on the occasion of Formatting titanium oxide and alkaline earth sulphate, or after this operation. In this last hypothesis, a dry impregnation of one or more solutions of salts metal is preferred, the preparation conventionally terminating with a treatment thermal.
The composition or collection mass may be in any known form : powder, beads, extruded, monoliths, crushed material, etc. The preferred form is the extruded, whether it be cylindrical or polylobed. In the case of shaping followed by mixing an extrusion, the cross section of the extrudate is advantageously between 0.5 and 8 mm, from preferably between 0.8 and 5 mm.
According to the invention, the use of the capture mass is carried out either in a bed reactor fixed, either in a radial reactor, or even in a fluidized bed, with or without use dispenser tray.
The conditions of use are such that the pressure is between 0.5 and 10 MPa, preferably between 1.5 and 3.5 MPa, and even more preferably between 2.0 and 3.0 MPa, the temperature between 100 and 350 C, preferably between 100 and 250 C.
After removal of the halogenated compounds, the purified gas has a content residual halogenated compounds of less than 10 ppb wt or even 5 ppb wt for each component.
In addition, the uptake of halogenated impurities has no impact on catalytic properties of the composition towards the hydrolysis reactions of COS and HCN, the solid keeping his initial activity.

= 10 This mass can be used in gas purification implemented in the installations of cogeneration. In cogeneration plants, synthesis gases are usually implemented at a pressure of between 1 and 10 MPa, and at a temperature of between 100 and 280 C.
The solid can also be used to eliminate halogenated compounds present in the gases implemented in chemical synthesis units, such as synthesis of methanol. In the most recent processes, the synthesis of methanol is usually put at a pressure of between 1 and 15 MPa, preferably between 5 and

10 MPa and at a temperature between 150 and 300 C, preferably between 220 and 280 C.
Advantageously, the use of the capture mass is carried out upstream of a Fischer-Tropsch synthesis unit which is generally implemented under a pressure between 0.1 and 15 MPa, preferably between 1.5 and 5 MPa and at a temperature between 150 and 400 ° C., preferably between 170 and 350 ° C.
The Fischer-Tropsch synthesis unit operates either in a fluidized bed or in a bed fixed (reactor containing a fixed bed catalyst or several beds of catalyst in the same reactor), or in a three-phase reactor (implementation in "slurry" according to the terminology in English) comprising the catalyst in suspension in a liquid phase essentially inert and the reactive gas phase (synthesis gas).
The catalyst used for Fischer-Tropsch synthesis is generally a catalyst containing cobalt or iron, whether supported or not, the support being preferentially chosen among the oxides of the group formed by alumina, silica, zirconia, oxide of titanium, the oxide magnesium or mixtures thereof.
Use of the capture mass to eliminate halogenated compounds a gas of synthesis is particularly suitable when the catalyst used for synthesis Fischer-Tropsch comprises cobalt, for example supported on alumina.

11 In general, the invention relates to the use of said composition jointly as a capture mass for removing halogenated impurities such as HF, HC1, HBr or HI contained in a gaseous mixture and as a catalyst for achieve hydrolysis of COS and / or HCN.
Examples;
Example 1 (according to the invention):
A composition comprising 85.5% by weight of TiO 2, 0.5% by weight of Al 2 O 3, 10% by weight of CaSO4. This is in the form of extrusions 2 mm in diameter. The composition is used in a fixed bed reactor to purify a synthesis gas containing approximately 61% volume of CO, 19% volume of H2, 10% volume of N2 and 10%
volume of CO2 as major components, as well as impurities at contents of 5 ppm by weight of HC1, 0.8 ppm by weight of HF, 4 ppm by weight of HBr, 1.5 ppm by weight of HI
10000 ppm weight of H2S, 1200 ppm weight of COS, 100 ppm weight of HCN, and 3 ppm weight of NH3.
The conditions of use are as follows:
Temperature: 180 C
Pressure: 2.3 MPa Hourly Volumetric Speed (VVH): 2500 The composition of the gas before and after purification is given in the table 1.
Table 1 Impurities present in content (ppm weight) content (ppb weight) the gas before purification after purification H2S 10000 Not analyzed NH3 3 Not analyzed COS 1200 <5 HCN 100 <5 HC1 5 <5 HF 0.8 <5 HBr 4 <5 HI 1.5 <5 =
= 12 The results in Table 1 show that the halogenated compounds initially present were completely removed from the treated gas. In addition, the use of the composition also have allowed to hydrolyze both COS and HCN impurities. The capture of compounds therefore halogenated did not have any effect of deactivation of the solid vis-à-vis the catalysis hydrolysis reactions of COS and HCN.
Moreover, the mass of capture used was analyzed by a technique semi-quantitative based on X-ray fluorescence analysis. The composition of the mass before and after use is given in Table 2. It can be seen that the impurities halogenated gases initially present in the gas to be treated were trapped on the solid.
Table 2 content (% weight) content (% by weight) Halogenated impurities before use after use Fluorine Not detected 0.05 Chlorine Not detected 0.3 Iodine Not detected 0.1 Bromine Not detected 0.24 Example 2 (according to the invention):
A composition comprising 85.5% by weight of TiO 2, 0.5% by weight of Al 2 O 3, 10% by weight of CaSO4. This is in the form of extrusions 2 mm in diameter. The composition is used in a fixed bed reactor to purify a synthesis gas containing approximately 36% volume of CO, 24% volume of H2,20% volume of H20 and 18,5 %
volume of CO2 as major components, as well as impurities at contents of 25 ppm weight of HC1, 1.5 ppm weight of HBr, 10000 ppm weight of H2S, 800 ppm weight of COS, 640 ppm weight of HCN, and 2000 ppm weight of NH3.
The conditions of use are as follows:

=

Temperature: 190 C
Pressure: 2.5 MPa Hourly Volumetric Speed (VVH): 4000 h-1.
The composition of the gas before and after purification is given in the table 3.
Table 3 Impurities present in content (ppm weight) content (ppb weight) the gas before purification after purification H2S 10000 Not analyzed NH3 2000 Not analyzed COS 800 <5 HCN 640 <5 HC1 25 <5 HBr 1.6 <5 The results in Table 3 show that the halogenated compounds initially present were completely eliminated. The use of the composition also allowed eliminate jointly COS and HCN. There is no deactivation of the solid relative to its properties of catalyzes the hydrolysis reactions of COS and HCN.
Moreover, the mass of capture used was analyzed by a technique semi-quantitative based on X-ray fluorescence analysis. The composition of the mass before and after use is given in Table 4. It can be seen that the impurities halogenated gases initially present in the gas to be treated were trapped on the solid.
Table 4 content (% weight) content (% weight) Halogenated impurities before use after use Chlorine Not detected 0.18 Bromine Not detected 0.012

Claims (10)

14 1. Using a composition upstream of a Fischer-Synthesis Unit Tropsch, and together as a capture mass to remove halogenated impurities contained in a gaseous mixture and as a catalyst for carrying out the hydrolysis COS and / or of HCN, said composition comprising between 30% by weight and 99% by weight of TiO2 and enter 1% by weight and 30% by weight of at least one sulfate of an alkaline earth metal selected among the calcium, barium, strontium and magnesium. 2. Use according to claim 1, wherein the impurities halogenated include HF, HCl, HBr and / or HI. 3. Use according to claim 1 or 2, wherein said composition includes between 3% by weight and 25% by weight of at least one sulphate of an alkaline earth metal chosen from calcium, barium, strontium and magnesium. 4. Use according to any one of claims 1 to 3, in which said sulfate is calcium sulphate. The use according to claim 4, wherein said composition understands between 60% weight and 95% weight of TiO2. 6. Use according to any one of claims 1 to 5, in which said composition further comprises at least one compound selected from clays, silicates, aluminas, titanium sulphate, ceramic fibers to a total content between 0.1% by weight and 30% by weight. 7. Use according to any one of claims 1 to 6, in which said composition further comprises 0.1% by weight and 20% by weight of a compound doping or a combination of doping compounds selected from iron compounds, vanadium, cobalt, nickel, copper, molybdenum and tungsten. Use according to claim 7, wherein the compound (s) dopants are under form of oxides or sulfides. 9. Use according to any one of claims 1 to 8, in which the composition or capture mass is shaped by extrusion. 10. Use according to any one of claims 1 to 9, in which mixture gas is a synthetic gas containing, before contact with the composition, one content of halogenated compounds of between 0.1 ppm by weight and 1000 ppm by weight.